This invention relates to alarm units and, more particularly, to portable alarm devices for personal use.
A large number of portable personal alarm devices have been devised in recent years in an effort to provide people with security against personal attack by criminal elements. Additionally, these devices can provide an effective means of signaling for help when a person is injured or incapacitated from non-criminal means. These devices fall into two basic categories.
One category of alarm device requires the user to carry a transmitter which sends an alarm signal to a remote receiver--for example, a police station or a nurse's station in a hospital. Examples of the transmitter type of personal alarm are disclosed in U.S. Pat. No. 4,189,721 of Doell. This first type of device suffers from the disadvantage that it requires that assistance be obtained only from people at the remote location. Thus, people who are closer to the user, and capable of more rapid response, may be totally unaware of the signal. Nevertheless, these devices have value in that the transmitters are generally light weight and small in size.
The second general type of personal alarm is a device which emits an audible signal when a person is in trouble, either due to natural accidental causes or criminal involvement. Examples of this second type of device include those disclosed in U.S. Pat. No. 4,158,197 of Takagaki, U.S. Pat. No. 4,151,520 of Full, and U.S. Pat. No. 4,520,351 of Altman et al. These devices require a size-sound level tradeoff. In particular, the greater the sound produced by the device, the larger the device usually is. Such large devices are cumbersome and owners are reluctant to carry them. Further, their physical size makes it difficult for the user to activate them in an emergency situation. For example, they may be stored in a woman's purse or a travel case and it would be necessary to remove the device from its case prior to activation. When smaller devices are used the sound level is generally of such a low level that they are relatively ineffective. Typically, criminal attacks do not occur when a person is in close proximity to others and there is little need to summon aid to a person in distress when he is in the near vicinity of other people.
Another difficulty with the bulky personal alarms, such as that in the Altman et al. patent, is that they are difficult to conceal. Therefore, during an attack a perpetrator can seize the alarm device and turn it off or destroy it before help is summoned. Thus, an easily disguised small package is preferred.